Tax invoice for goods sent to exhibition for display/ sale- interstate

A fashion designer participates in exhibitions in different states and obtains casual registration. She sends goods to the exhibition under e-way bill primary for display and get orders for supply later. In the process, she also makes some local sales on the spot at the exhibition and issues tax invoice for the same under casual registration. All unsold goods are returned to her by e-way bill from exhibition. I want to know if it is necessary for her to also raise a tax invoice from her main location to casual registration number for goods sold at the exhibition as the same are not returned to her main location, having been sold there. Or is there any requirement of any other documentation? 

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